Mafic dykes of Almora region intrude the Precambrian crystalline rocks of Kumaun Lesser Himalaya. Mafic dykes exhibit fine grained margin and medium to coarse grained core, melanocratic, low to highly ferromagnetic (MS=0.85-38.58×10 -3 SI) in nature commonly showing subophitic to ophitic textures with ol-pl-cpx-hbl-bt-mt-ap-sp assemblage, and modally correspond to leucogabbro and olivinegabbro (sensu stricto). Olivine (Fo 61 -Fo 33 ), clinopyroxene (Wo 46 -En 42 -Fs 22 to Wo 40 -En 36 -Fs 15 ) and plagioclase (An 58 -An 12 ) have crystallized in the temperature range of ca1400-980 o C at pressure <2 kbar in an olivine tholeiitic basalt parent. Low acmite (Na pfu =0.033-0.025), (Mg # =0.64-0.82), Ti-Al contents of clinopyroxenes and their evolution along enstatite-ferrosilite join (i.e. MgFe substitution) strongly suggest tholeiitic nature of mafic dyke melt with changing activities of alumina and silica. Clinopyroxene compositions of mafic dykes differ markedly as compared to those observed for adjoining Bhimtal volcanics but closely resemble to that crystallized in tholeiitic melts of Deccan province. Observed Cr vs Mg # variation, enriched LILE (Sr, Ba)-LREE and positive Eu-anomaly of the studied mafic dykes are indicative of fractional crystallization of olivine-clinopyroxene -plagioclase from a crustally-contaminated tholeiitic basalt magma derived from enriched mantle source. The mafic dykes of Almora are geochemically identical to mafic dykes of Nainital, but are unrelated to Precambrian mafic volcanic flow and dykes of NW Himalaya and dykes of Salma and Rajmahal regions.

Petrography and stable isotopic (carbon and oxygen) studies of the Middle Eocene of Garampani limestone from Jamunagar limestone quarry of the Umrangso area, North Cachar Assam, were carried out to determine the environment of deposition and the level of diagenesis to improve our understanding of the climate at the time of formation. The major petrographic types documented here are include wackestone, packstone and grainstone which fall into the type I and II categories of the triangular classi cation scheme indicating formation in a shortlived, high-energy environment that was dissipating at the time of deposition. The samples have a distinct signature that includes extensive diagenesis with varying intensities of compaction, recrystallization, pressure solution, and neomorphism. Most of the samples produced positive δ 13 C ‰ ranges from 1.64 to 0.76‰ (PDB) and correlated with a transgressive phase. The negativeδ 18 Ovalues range from − 6.25 to -4.67‰ (PDB) suggesting that the Middle Eocene was generally characterized by a warmer climate.

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